Third-generation mobile systems (3G) based on WCDMA radio-access technology are being deployed on a broad scale all around the world. Knowing that user and operator requirements and expectations will continue to evolve, the 3rd Generation Partnership Project (3GPP) has begun considering the next major step or evolution of the 3G standard to ensure the long-term competitiveness of 3G. The 3GPP launched a Study Item “Evolved UTRA and UTRAN” (E-UTRA and E-UTRAN), that will investigate means of achieving major leaps in performance in order to improve service provisioning and reduce user and operator costs.
A system with evolved radio access, like in E-UTRA, shall operate in frequency spectrum allocations of different sizes both in uplink and downlink direction, e.g. 1.25 MHz, 2.50 MHz, 5.00 MHz, 10.00 MHz, 15.00 MHz and 20.00 MHz, like suggested in 3GPP TR 25.913, “Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN)”, version 7.3.0 (available at http://www.3gpp.org). E-UTRA should be able to operate in a standalone manner, namely without utilizing other carriers than the defined frequency spectrum.
On the other hand, user terminals (UE) themselves have pre-defined frequency bandwidth capabilities that usually are different to that of the system's utilized frequency range. The frequency bandwidth capability of a UE defines the frequency range which a UE can utilize for communicating, i.e. to send and receive data. As there are various types of UEs with different bandwidth capabilities as well as various cells with different frequency bandwidth sizes, it must be assured that every UE can establish a radio link with every kind of cell.
Consequently, for each of these system bandwidth sizes it is respectively possible to define several UE deployments. The UE covers only a specific part of the system's frequency range, wherein the covering is called “UE camping”, and the UE tunes its carrier frequency to an appropriate center frequency within the system bandwidth to send and receive data.
The system's frequency range is illustrated in FIG. 1, in this case 20 MHz, further comprising possible camping positions of UEs with capabilities in the frequency domain of 5, 10, 15 and 20 MHz. More specifically, according to the illustration, the system bandwidth is divided into subbands of uniform size. It should however be noted that also subbands of non-uniform size may be defined within the system bandwidth. User terminals with lower bandwidth capabilities can be deployed on more positions in comparison to terminals with higher bandwidth capabilities.
For example, as apparent from FIG. 1, a UE with a 15 MHz capability, denoted a 15 MHz UE, has three possible camping positions, whereas a 5 MHz UE has seven possible deployments within the system bandwidth. Moreover, a 15 MHz UE naturally covers more bandwidth than a 5 MHz UE, thereby providing a broader coverage for receiving and transmitting data.
Further, the UE must be in an active state with the 3GPP interface (e.g. LTE_Active) in order to be able to send and receive user data. In this state a radio connection is established and the UE reports measurements and requirements to its current base station. Then, bearers are established between the UE and the network, carrying first the signaling and later the user data.
During mobility in active state, the UE continuously measures the signal strength of neighboring cells and sends measurement reports to the network. When the network decides to use a new base station, it establishes a new radio link and triggers the UE to handover to the new base station.
In addition to the active state, a mode with lower power consumption is supported. This mode is called idle state (e.g. LTE_Idle) and is used when no user data is sent or received. In idle state the cell reselection is performed by the UE and only tracking area (TA) changes are registered with the network (i.e., not every cell change is reported to the network). The network does not know the actual location of the UE on cell-level, but only on TA-level. In idle state most of UE related contexts are deleted in the 3GPP radio access network (RAN) and it is further possible to page the UE in order to perform transition from LTE_Idle to LTE_Active.
A UE in LTE_Idle state has to receive broadcast cell search parameters and paging information. By standard these relevant cell parameters are transmitted via the paging and broadcast channels, broadcasted in the central band of the cell bandwidth as a default location in the frequency plane, so that all UEs know at which frequency to receive this information. However, any other default frequency band may be defined for transmitting cell broadcast data. For further illustration of the present invention it is assumed that said default frequency subband is the central band of the system bandwidth.
The UE has to be deployed in said central band when in LTE_Idle state. According to FIG. 1, this might be a 5 MHz wide band with its center frequency being equal to the center frequency of the complete system bandwidth of 20 MHz. Consequently, UE camping positions available for deployment in LTE_Active and in LTE_Idle mode are marked with a dark grey, whereas camping positions for deployment in only LTE_Active mode are illustrated in light grey. In particular, assuming the system bandwidth of 20 MHz, shown in FIG. 1, 5 and 10 MHz UEs have only one possible camping position for LTE_Idle and seven, respectively three LTE_Active camping positions.
FIG. 2 shows an exemplary distribution of various traffic channel types in different subbands of a 15 MHz bandwidth system. More specifically, user data traffic in the user plane can be sent and received in every subband of the system via dedicated Radio Bearers, that are established and then notified to the UE. Accordingly, a specific subrange within the subband is assigned to a specific UE in order to transmit to and receive data from the UE.
In addition, other RRC message Radio Bearers for control plane traffic may also be allocated in every subband of the system bandwidth. On the other hand, as a Multimedia Broadcast/Multicast Service (MBMS) has to be received by UEs of all capabilities being in the LTE_Idle state, the service is only transmitted in the central band. In addition to multicast traffic, also broadcast and paging control plane traffic on the downlink has to be transmitted in the central band. It is clearly apparent that the traffic density, measured per frequency unit, is higher in the central band relative to traffic density in the side bands.
The paging procedure is used to transmit paging information to selected UEs in idle mode using the paging control channel (PCCH). This channel is used when the network does not know the location cell of the UE, or the UE is in the cell connected state but utilizing UE sleep mode procedures. Furthermore, upper layers in the network may request paging, to e.g. initiate and establish a signaling connection to the terminal. UTRAN may initiate paging for UEs to trigger a cell update procedure or the reading of updated system information. UTRAN may also initiate paging for UEs to release an RRC connection.
Several transport channels are necessary and provided for the implementation of the paging procedure. In particular, the main channels are the Broadcast Channel (BCH), the Paging Indicator Channel (PICH) and the Paging Transport Channel (PCH).
The BCH is a transport channel that is used to transmit information specific to the E-UTRA network or for a given cell. The most typical data needed in every network is the available random access codes and access slots in the cell, or the type of transmit diversity method used with other channels including PCH and PICH for that cell. As the UE cannot camp to the cell without the possibility of decoding the broadcast channel, this channel is needed for transmission with relatively high power in order to reach all the users within the intended coverage area.
The PICH is operated together with the PCH to provide terminals with efficient sleep mode operation through paging. The PICH informs the terminal via Paging Indicators (PIs) about relevant paging messages that are to be transmitted via the PCH. It should be noted that said paging messages may be alternatively transmitted via downlink shared transport channel (DL-SCH). The former option will be assumed throughout the invention without loosing generality. Each PICH frame carries 288 bits to be used by the paging indicator, whereas 12 bits are left idle for future use. Depending on the PI repetition ratio, there can be 18, 36, 72 or 144 paging indicators per PICH subframe. More specifically, the PIs are assigned to a paging group, and a terminal, once registered to a network, has been allocated a paging group. The PIs appear periodically on the PICH when there are paging messages for any of the terminals belonging to that paging group. In LTE further solutions assuming direct reading of paging messages without PICH usage are possible, but will not be discussed herein, because it does not implicate any changes for the present invention.
The PCH is a downlink transport channel that carries data relevant to the paging procedure, in this case the actual paging data message. In a cell, a single or several PCHs may be established. Each Secondary Common Control Physical Channel (SCCPCH) indicated to the UE in system information may carry up to one PCH. Thus, for each defined PCH there is one uniquely associated PICH channel also indicated.
The frequency subband that is to be used for paging is notified to the UE on the BCH in so called System Information Blocks (SIBs). For example, System Information Block Type 5 comprises the configuration parameters for the PICH and PCH. SIBs usually group together information elements of the same nature. Dynamic parameters are grouped into different SIBs from the more static parameters. The SIBs are organized as a tree, whereas a Master Information Block (MIB) gives references and scheduling information to a number of system information blocks. Furthermore, MIB also comprises timer information about dynamic parameters, to trigger a re-reading by the UE when the timer lapse. The MIB is sent regularly on the BCH and its scheduling is static.
The paging itself is initiated by Paging Indicators (PIs) that are transmitted on the physical channel, PICH. The terminal at first camps in the central band of the system bandwidth and receives cell broadcast information via the BCH. As already mentioned a UE then knows on which frequency the PIs and the paging data message is to be transmitted. Subsequently, the UE periodically listens to the PICH whether relevant PIs are being transmitted.
Once a relevant PI has been detected by the UE, the UE decodes the next PCH frame, mapped on the SCCPCH, to see whether the paging message is intended for it. Accordingly, the paging message comprises, among other information, the International Mobile Subscriber Identity (IMSI) of the mobile terminal, by which the terminal is enabled to discern whether the paging message is indeed intended for it or not.
The less often the PIs appear, the less often the UE needs to wake up from the sleep mode and the longer the battery life becomes. The trade-off is obviously the response time to the network-originated call.
The paging message itself may be expanded relative to paging messages in previous systems. For example, uplink interference information as in SIB7 may be additionally included. For the further illustration of the underlying problem and also for the embodiments of the invention it is assumed that the size of the paging message is two Resource Blocks. The assumed amount of two Resource Blocks for one paging message is however just an example used for the illustration of embodiments. A skilled person is also able to apply the teachings of the various embodiments to paging messages split into a different number of Resource Blocks.
A Resource Block is defined in the frequency-time domain as may be appreciated in FIG. 2. The Resource Block is a specific time-slot (subframe) for a specific frequency subrange within the system bandwidth used for transmitting data. Within the Resource Block data may be transmitted, which is limited by the length of the subframe (˜0.5 ms) and the frequency bandwidth (˜375 kHz). Naturally, both the length of the subframe and the bandwidth can be adapted by a skilled person to the necessities of the specific implementation without relevant effect on the invention's embodiments. Furthermore, it is also possible to encode the data transmitted in the Resource Block to specific mobile nodes, similar to CDMA. Though not explicitly explained in regard to the various embodiments of the invention it is further possible for a skilled person to implement such a code multiplexing to the embodiments of the present invention.
A further important transmission option is the specific diversity technique, implemented for improving the reception quality of a transmitted signal. In a Resource Block, the amount of frequency diversity is small, namely about 375 kHz. It is widely known that by receiving and processing multiple versions of the same transmitted signal the reliability of the message reception may be improved. Different diversity techniques are possible which are mainly characterized by the way the signals are received. This includes among other options: space diversity, polarization diversity, time diversity or frequency diversity. For the following, only time and frequency diversity are relevant and hence will be briefly explained in further detail.
In using the time diversity technique, the same signal is received more often, due to the transmission of the signal at different time instances. The signal is transmitted in multiple subframes that are separated by a pre-determined coherence time. This technique is easy to implement, however, the terminal has to wait for the diversity repetition of the signal. Hence, the delay of the mobile node, for moving from a camped state, LTE_Idle, to an active state, LTE_Active, such that a user traffic plane is established, is increased.
The frequency diversity relies on the fact that the noise of signals transmitted at different carrier frequencies is not correlated. Therefore, the same signal may be transmitted via multiple channels separated by a specific bandwidth, to improve the reception of the message.
Subsequently, the received multiple signals have to be combined within the terminal to achieve a higher reliability resulting from the thus improved signal. As this is however not relevant for this invention, no further details are discussed in this regard.
FIG. 3 shows a usual frequency allocation for the paging data message in a paging procedure, in which the configuration of the PCH, carrying the paging message is static and cannot be changed. In this example, the system has a bandwidth of 20 MHz and two different UE capabilities of 10 and 15 MHz are considered. Apparently, the frequency range covered by both UEs comprises the central subband, subband 2. The paging data message, consisting of Resource Blocks 1 and 2, is transmitted in the central subband, and accordingly received by both UEs. In addition, a frequency diversity repetition is transmitted to increase the signal reliability in the recipients, the UEs. Accordingly, in left subband 1 the paging message, Resource Blocks 1 and 2, is transmitted again within the same subframe. However, the total transmission frequency range within one subframe is now 15 MHz, meaning that the subframe with the two paging messages cannot be received by the 10 MHz UE. Therefore, to achieve relatively reliable transmission of paging for this category of mobile terminals, it is required to repeat both Resource Blocks of the paging message in the time domain after at least maximum coherence time, corresponding to mobile radio channels of UE population. Hence, if the message is received correctly after the time diversity, delay of session setup procedure for network-originated scenarios is increased by the value of the coherence time.
In addition to the disadvantage that not only the latency of the session setup for moving from the LTE_Idle state to the LTE_Active state is increased for terminals of lower capability, a further disadvantage occurs. The resources of the central subband 2 and side subband 1 are used inefficiently, as Resource Blocks of the paging message are repeated in subband 1 to achieve diversity in the frequency domain and in subband 2 to achieve diversity in the time domain.
As already outlined above, a fixed paging procedure has been defined in the prior art. Thus the paging cannot be changed depending upon certain system parameters, which may include the traffic densities in respective frequency subbands, UE bandwidth capability, information importance or other parameters.